Mobile communication networks generally include base stations transmitting and receiving radio frequency (RF) signals from a plurality of mobile devices (e.g., cellular telephones). Typically, the base station instructs the cellular telephones how much power to utilize when transmitting RF signals. The base station determines the amount of power a particular cellular telephone should utilize based upon the distance the cellular telephone is from the base station. For example, the farther the cellular telephone is away from the base station, the more power the cellular telephone needs to utilize in transmitting the RF signals. Likewise, when the cellular telephone is close to the base station, the cellular telephone needs to utilize less power in transmitting the RF signals.
Cellular telephones typically include one or more power amplifier (PA) line-ups. In Global System for Mobile communications (GSM) modulation cellular telephones, there are typically two PA line-ups: one line-up for low frequency band signals (e.g., 824 megahertz (MHz) to 915 MHz), and one line-up for high frequency band signals (e.g., 1710 MHz to 1910 MHz). Current PA line-ups are designed so that they achieve maximum power added efficiency (PAE) at peak radio frequency power levels. In other words, current PA line-ups are designed to most efficiently utilize battery power when they are operating at their peak power level, which is approximately 33 dBm. For example, when operating at approximately 33 dBm, cellular telephone power amplifier modules typically have a PAE in the range of about 40-45%.
When a cellular telephone is located at a distance where the base station instructs the cellular telephone to operate at less than 33 dBm, the cellular telephone will begin to be even less efficient than the 40-45% PAE discussed above. One method of improving the PAE at medium to high power levels (e.g., >20 dBm) includes tuning the impedance of the various components within the PA line-up. However, at low power levels (e.g., <20 dBm), the PAE cannot be improved by simply impedance matching the various components within the PA line-up, which results in a low PAE at low power levels. For example, when operating at less than 15 dBm, the PAE of typical PA line-ups is approximately 1%-5%, which is significantly lower than the 40%-45% when operating at 33 dBm.
Since many cellular telephone users reside in urban areas, multiple base stations are required to accommodate the large volume of cellular telephone traffic. This results in urban areas including a relatively large number of base stations within a relatively small geographic area. Thus, for some cellular telephone users they may rarely be located far enough away from a base station to operate at their maximum power level (and maximum PAE). Accordingly, these cellular telephones will be operating at a less than optimal efficiency level the majority of the time. Moreover, it has been determined that most cellular telephones operate at their peak power level less than 5% of the time, which results in cellular telephones are outputting low levels of power (e.g., <20 dBm) greater than 95% of the time. The result of this situation is an overall low average PAE for PA line-ups and a shortened battery life for many cellular telephones. Accordingly, it is desirable to provide apparatus and methods for more efficiently utilizing battery power when a cellular telephone is operating at less than its maximum power level. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.